In a thin film transistor using a semiconductor, a semiconductor thin layer is layered on the surface of an insulator and electrons or holes move through the semiconductor thin layer in the vicinity of this interface between the insulator and the semiconductor. In the case of an organic semiconductor material, the organic semiconductor material is heated to evaporate and attach the material to the surface of an insulator. At this time, the microscopic surface state of the insulator, in detail, surface roughness, substances adsorbed on the surface, surface molecular defect and the like affect the performance of the thin film transistor and significantly deteriorates the performance in many cases. In addition, a coating method is known in which a solution prepared by dissolving an organic semiconductor material in a solvent is coated on the surface of an insulator and the solvent is removed so as to form a thin film composed of the organic semiconductor material. This coating method is for easily spreading out the solution on a large-area substrate and thus to achieve a large-area organic electronic device. However, the solvent used in the coating method changes the nature of the surface of the insulator substrate and deteriorates the interface, and thus the organic thin film transistor fabricated have a decrease in performance such as an increase in driving voltage or an increase in leakage current in some cases.
In order to prevent such a decrease in performance, attempts to homogenize the surface and the interface after layering by subjecting the surface of the insulator substrate to a special surface treatment have been made. More specifically, a method is known in which a self-assembled monolayer (hereinafter, also referred to as SAM) is formed at the interface between the insulator and the organic semiconductor.
However, a SAM having a thiol group (—SH) of the related art can be formed only on a limited surface of a metal such as gold, or the like.
In addition, a SAM material having a phosphoric acid group or a phosphonic acid group has recently been proposed (see Non Patent Literature 1).
This novel SAM material interacts with a wide variety of metal oxide surfaces and is able to form an organized monolayer. However, the formation of the SAM on the surface of organic materials is limited.
As described above, the SAM material of the related art can be formed on a limited surface and is also greatly affected by the surface state. Particularly, in the case of employing a metal oxide as an insulating layer to form an organic semiconductor, a trouble that a SAM is not normally formed due to the unevenness of the surface tends to be caused and there is a problem that inferior quality is unavoidable when a SAM is applied to a large area in particular.
As described above, although the quality management at the interface between the insulator and the organic semiconductor is important in a thin film transistor, an additional treatment complicates the manufacturing method and also there is a problem that the quality management is difficult. Furthermore, there is also a problem that the expected properties are exhibited in the earlier stage after the fabrication but the interface changes along with the drive of the device, and the performance changes and deteriorates with the elapse of use time.
In addition, it is possible to impart a specific function to the surface of a solid substrate by bonding a functional group exhibiting functionality to a moiety of the molecule forming the SAM. For example, it is possible to impart various functions such as electron transfer and oxidation-reduction reactions, catalysis, light-induced electron transfer, electrochemical luminescence, recognition of ions and molecules, bio-sensors, bio-molecular devices, and photovoltaic power generation to the surface of a solid substrate by the formation of a SAM, and the application of a SAM in these fields is expected.
For example, formation of a SAM using, as a material, an alkylenethiol compound having an amino group as an end group for fixing a saccharide having an aldehyde moiety or a compound having a carboxyl group (see Patent Literature 1), formation of a SAM using an alkylenethiol compound having an electron accepting functional group such as a cyano aryl group at an end group, and the like as a material (see Patent Literature 2), formation of a SAM exhibiting ultraviolet resistance using an alkylenethiol compound having a polyphenylene group at an end group, and the like as a material (see Patent Literature 3), formation of a SAM having a rigid adamantane surface film structure using bis(adamantylmethyl)disulfide (see Patent Literature 4), formation of a SAM for lithography that is able to be patterned with light having a long wavelength by the introduction of a functional group sensitive to light having a relatively long wavelength in the middle of an alkylene chain (see Patent Literature 5), formation of a SAM for a photovoltaic cell and a photocharge separating element using a compound obtained by covalently bonding a pyrrole ring-expanded porphyrin and a fullerene (see Patent Literature 6), and the like have been reported.